BASIC AC Flashcards
More than ______ of electric energy is generated by AC machines
90%
AC generation can be accomplished economically in _____ power plants that may be located where fuel and water are abundant
LARGE
Types of industry that a great portion of the AC energy is converted to DC
- Railway Transportation
- Communication System
- Home
- Electrochemical Industry
- Motor Applications
AC/DC Power Supply
AC Supply -> Transformer -> Rectifier -> Smoothing (Filter/Capacitor) -> Regulator -> Load
Why is AC generation more ideal than DC generation?
Because DC can’t be stepped down or stepped up. In order to step up or down a DC, we need to convert it first to AC which is feasible but expensive.
In DC systems, energy must be transmitted from generator to consumer at essentially the same EMF as it is generated; this is usually restricted to such low values as _____, ______, and ______.
250V, 600V, 1500V
Two effects of having lower current thru the transmission line due to stepping up of voltage via transformer
- Lower line losses (I²R) over long distances (reduce copper loss)
- Lesser diameter transmission wires needed (save copper)
T or F. Transformer has no moving parts.
TRUE
In GMEC, 18kV is stepped up to _______
230kV
AC generator is also referred to as ______
ALTERNATOR
When the wire loop or coil rotates one complete revolution, or 360°, _______ is produced
ONE FULL WAVEFORM
It is the time interval between two occurrences of the wave
PERIOD (T)
It is the number of oscillations (cycles) that take place in a given amount of time
FREQUENCY (f)
It is the angular displacement of any element of the wave per unit of time or the rate of change of the phase of the waveform
ANGULAR FREQUENCY (ω)
T or F. Electrical angle is a degree.
FALSE.
RADIAN
π rad is equal to _____
180°
Average voltage in a complete/full sine wave or one full cycle
ALWAYS ZERO
It is the area under the curve within a given time period
AVERAGE VALUE
It is the square root of the average (mean) of the square of the alternating amplitude values
EFFECTIVE/RMS VALUE
It is defined as the AC value that will give the same heating effect as an equivalent DC voltage
EFFECTIVE/RMS VOLTAGE
The measure of the extent that a graph of the sinusoidal function is moved horizontally to the left or to the right
PHASE SHIFT (φ)
φ can be determined by measuring the shift of the _________ of the wave.
POSITIVE SLOPE ZERO CROSSING
Sinusoid is shifted to the left when phase shift is positive
SINUSOIDS LEADS THE REFERENCE
Sinusoid is shifted to the right when phase shift is negative
SINUSOIDS LAGS THE REFERENCE
T or F. The slower the rotor rotates, the more cycle per second of voltage is induced
FALSE
FASTER (speed of rotation ∝ frequency)
T or F. Frequency is also directly proportional to the number of main field poles
TRUE
Electrical degrees relate to _______ of the sinusoid
ELECTRICAL FREQUENCY
Mechanical degrees relate to ______
MECHANICAL ROTATION
T or F. In a 2-pole alternator, one electrical cycle is formed in one mechanical revolution
TRUE
In a _____ alternator, two electrical cycles are formed in one mechanical revolution
4-POLE
The governing principles on the relationship between electrical frequency and speed rotation for single phase alternators apply to ________ alternators.
3-PHASE
Scalar quantities are numbers that have ______
MAGNITUDE BUT NO DIRECTION
Vector quantities indicate ______
MAGTINUDE AS WELL AS DIRECTION
The association that recommended the term phasor instead of vector to be applied to lines that are given direction wrt a reference when they are used to replaced sinusoidal functions
AMERICAN STANDARDS ASSOCIATIONS (ASA)
T or F. A phasor is a vector.
FALSE
NOT
I = 200∠60° Amps
POLAR FORM
I = 100 + j173.21 Amps
RECTANGULAR FORM
A _____ may be specified by the magnitude of its projection on the x and y axes
PHASOR
Methods to derive the resultant of phasors
TIP-TO-TAIL METHOD
COMPONENT-BREAKDOWN METHOD
T or F. In a transformer, the voltage frequency at the primary side is not always the same as the voltage frequency at the secondary side
FALSE
ALWAYS
T or F. Np < Ns - step down transformer
FALSE.
STEP UP
Ip > Is
STEP UP TRANSFORMER
Vp > Vs
STEP DOWN TRANSFORMER
n>1
STEP DOWN
n<1
STEP UP
It steps up the 18kV plant-generated voltage to the transmission voltage of 230kV
GMEC GSUT (Generator Station Unit Transformer)
It steps down the 18kV plant-generated voltage to the auxiliary load voltage of 6kV
GMEC UAT (Unit Auxiliary Transformer)
It steps down the 230kV transmission line voltage to the auxiliary load voltage of 6kV
GMEC S/SAT (Start-up/Standby Auxiliary Transformer)
During _____ or ______, GMEC S/SAT is used in case plant generator has no output
SHUTDOWN or INITIAL STARTUP
What is the generator output voltage of GNPD?
26kV
SDAT stands for ____
STEP DOWN AUTO TRASFORMER
